The present invention relates generally to improvements in the accumulation, storage and dispensing of energy and it relates more particularly to an improved method and apparatus for the accumulation, storage and controlled release of thermal energy in which the thermal energy is stored in a medium which can be maintained in a high potential energy state for indefinitely long periods of time in uninsulated containers and may be controllably liberated at another time or another place and the heat storage medium thereafter recharged or reactivated by the application of heat to the medium.
At the present time, a major problem with the utilization of energy sources in which the rates of energy supply and demand cannot be matched for example heat sources such as solar and geothermal energy is the lack of an economical and efficient means of storing the energy for use at times other than the time of its availability or incidence upon the area of collection. A second major problem is an efficient means of transporting the received heat energy to a remote point of use. Until now, the means used for heat storage involved increasing the temperature of a medium and maintaining that elevated temperature until subsequent use of the heat. This practice requires heavily-insulated containers or conduits, which are expensive and result in large losses of heat energy even during short periods of storage or distribution. The mechanism now in use depends upon the storage of the heat either as sensible heat of a large mass or as latent heat of fusion of some suitable salt or other substance. Only modest amounts of heat may be stored in this manner per unit of mass or volume. The amount of heat stored in the conventional ways is a function of the temperature of the input and overall efficiency of collecting and accumulating the heat energy is inversely proportional to the temperature at which it is stored. For example, the efficiency of solar collector systems falls off very rapidly with increasing temperature because the reradiation of energy increases as the fourth power of the absolute temperature of the collector. Therefore, it is desirable to accumulate thermal energy at relatively low temperatures for improved collector efficiency.
On the other hand, it is usually desirable to utilize heat energy at as high a temperature as possible or desirable for the process in which it is used. In many processes, such as power generation, the efficiency of heat utilization is proportionate to the temperature of the heat source. In currently used methods of heat storage, as sensible heat or latent heat of fusion, the temperature of heat removal from the storage medium can never exceed that temperature at which the heat was stored, and cannot even equal it. Hence, a major difficulty with the present methods of heat storage is the low efficiency in either collecting or using the heat.